Compressors are often used in vehicles (e.g., superchargers) and in various industrial applications (e.g., screw compressors), and these compressors require effective shaft seals in order to seal a pressurized medium such as air or an exhaust-air mixture inside a given space. The shaft seals should also reduce or substantially prevent oil losses from the compressor. Shaft seals thus play an important role in providing an acceptably long service life for compressors, even under demanding operating conditions, while still protecting the environment in which the compressors are used by reducing the occurrence of oil leaks.
Designing an appropriate shaft seal for compressors is particularly challenging because the seal can be subjected to pressures of from zero to 0.5 MPa or higher which pressures may change rapidly and/or frequently. In addition, the shaft contacted by the seal may operate at very high rotational speeds—up to 25,000 RPM and above—and the relative speed between the seal element and the shaft can be more than 35 m/s.
Sealing assemblies for use under such conditions sometimes include PTFE seal elements. However, these conventional seals may wear too quickly and require service at relatively short intervals. Oil losses and/or gas leaks are also to be expected when conventional sealing assemblies are used.